This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 47990/2000 filed in Japan on Feb. 25, 2002, which is herein incorporated by reference.
The present invention relates to a vinyl polymer useful for forming an organic electroluminescent device excellent in heat resistance, a vinyl compound useful as a raw material of the vinyl polymer, and an organic electroluminescent device using the vinyl polymer.
An organic electroluminescent device (hereinafter, occasionally referred as xe2x80x9can organic EL devicexe2x80x9d) has been utilized in a display apparatus. In addition to properties such as high luminance (brightness), high light emission, full-colored display and durability, the organic EL device requires heat resistance (thermostability) because the device generates a large amount of heat when driving. In particular, when the organic EL device is used for interior lighting application and the like, it is predicted that a large amount of Joule heat is generated. Moreover, in the application such as an in-vehicle display, heat resistance is an important element because the surroundings may be exposed to high temperature. In this way, according to expansion of application of an organic EL device, it is practically important to improve heat resistance of an organic EL device.
An organic thin layer used for an organic EL device is usually an amorphous glass state from the viewpoint of mold-processability. Moreover, in order to make a device having high heat resistance, it is necessary to use an organic material having a high glass transition temperature for forming a thin layer.
Regarding a material for an organic EL device, before now, some kinds of materials forming an amorphous glass have been reported. However, in most of these amorphous materials, a glass transition temperature (Tg) thereof is low and not more than or about 150xc2x0 C. For example, as a hole-transporting material, compounds represented by the formulae (2a) to (2f) described below and having Tg of 75 to 151xc2x0 C. have been proposed. As an electron-transporting material, compounds represented by the formulae (3a) to (3c) described below and having Tg of 107 to 136xc2x0 C. have been proposed. Moreover, as a light emissive material, compounds represented by the formulae (4a) to (4c) described below and having Tg of 84 to 132xc2x0 C. have been proposed. Incidentally, the inventors of the present invention found the compounds (2a) to (2f), (3a) to (3c) and (4a) to (4c). 
Since these materials have low glass transition temperatures, it is difficult to improve heat resistance of organic EL devices obtained from these materials. Moreover, mold-processability is insufficient in these materials.
As a material for a polymeric organic EL device, there have been known a main chain-type polymer having a xcfx80-electron system in a main chain thereof, or a side chain-type polymer having a xcfx80-electron system in a side chain thereof. These materials are excellent in mold-processability. The main chain-type polymer, for example, includes materials represented by the following formulae. 
On the other hand, the side chain-type polymer has diversity of choices in a xcfx80-electron system chromophore constituting a side chain, and has superior chemical stability. Further, since an unconjugated-system structure in the side chain-type polymer is easily made in a main chain thereof, it is easy to impart mold-processability to the polymer. Moreover, the polymer has advantages such as excellent photoconductivity, and constant standard oxidation-reduction potential independent of doping rate. As such a side chain-type polymer, the inventors of the present invention have reported polymers comprising, as a side chain group having a xcfx80-electron system, carbazole, ferrocene, triphenylamine, pyrene, perylene, an oligothiophene and the like, and have clarified that these polymers are applicable to a cathode material for a secondary cell, a p-mode semiconductor material for a photoelectric transfer device, an electrochromic material and other materials [Synth. Met., 41-43, 3031 (1991), and literatures described therein, for example, Macromolecules, 28, 723 (1995); Synth. Met., 81, 157 (1996); Macromolecules, 30, 380 (1997); Synth. Met., 102, 969 (1999; and Electrochim. Acta. 45, 1543 (2000)]. However, even in the polymer materials described in these literatures, it is difficult to improve heat resistance due to their low glass transition temperature.
In this way, a polymeric material having a high glass transition temperature is required in order to improve heat resistance and mold-processability of an organic EL device.
It is, therefore, an object of the present invention to provide a vinyl polymer excellent in heat resistance and mold-processability and useful as a material for an organic EL device, and a vinyl compound useful for obtaining the vinyl polymer.
It is another object of the invention to provide an organic EL device having superior heat resistance.
The inventors of the present invention made intensive studies to achieve the above objects and finally found that a vinyl polymer, which is obtainable from a novel vinyl compound having a tris(biphenylyl)amine backbone as a side chain group having a xcfx80-electron system, is useful as a hole-transporting material for an organic EL device and has high heat resistance. The present invention was accomplished based on the above finding.
That is, the vinyl compound of the present invention is represented by the following formula (1): 
wherein R1 and R2 are the same or different, each representing a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.
In the above formula, the R1 and R2 maybe a hydrogen atom, a halogen atom, a linear or branched C1-6 alkyl group or a C1-6 alkoxy group. Preferably, the R1 and R2 may be a hydrogen atom, a C1-4 alkyl group or a C1-4 alkoxy group.
The vinyl compound may be represented by the following formula: 
wherein R1 and R2 have the same meanings defined above.
The vinyl polymer of the present invention has a unit represented by the following formula (2): 
wherein R1 and R2 are the same or different, each representing a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group.
The vinyl polymer may be a homopolymer of the vinyl compound, or a copolymer of the vinyl compound and a copolymerizable monomer. The glass transition temperature of the vinyl polymer may be about 200 to 250xc2x0 C. The number-average molecular weight of the vinyl polymer may be 5,000 to 500,000.
The present invention also includes an organic electroluminescent device comprising an organic layer between a pair of electrodes, and the organic layer comprises at least one layer containing the vinyl polymer. The organic layer may comprise a hole-transporting layer containing the vinyl polymer. For example, the organic layer comprises (1) a hole-transporting layer containing the vinyl polymer, a light-emitting layer and an electron-transporting layer, or (2) a hole-transporting layer containing the vinyl polymer and a light-emissive electron-transporting layer. The organic layer may further comprise an anode buffer layer.